1. Technical Field of the Invention
This invention relates generally to wireless communications and more particularly to measuring signal strength of received radio frequency signals.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is further known, the signal strength of a received RF signal may vary dramatically (e.g., by 100 dB). To accommodate such a large swing, the receiver includes automatic gain control (AGC) circuitry to adjust the gain of the low noise amplifier, the programmable gain amplifier, and/or digital gain within the data recovery stage depending on the signal strength of the received RF signal. For instance, the AGC increases the gain of the receiver such that it is sensitive enough to detect low power level signals and fast enough to adjust the gain of the receiver to a nominal level regardless of whether the received RF signal is a weak one or a strong one once the signal is detected.
For the AGC circuitry to work properly, it needs to receive an accurate measure of the power level of the received RF signal. Accordingly, most RF receivers include a receive signal strength indicator (RSSI) that measures the power level of the received RF signal. While there are numerous embodiments of an RSSI, they all suffer from process variations when implemented on an integrated circuit, especially when using CMOS technology. Thus, from chip to chip, the RSSI measures received RF signals differently. Generally, the RSSI is designed to accommodate for the variations, which limits the range of operation of the RSSI. Accordingly, other components within the receiver are also limited. For instance, with a limited RSSI range, the dynamic range of the ADC is limited, which reduces the resolution of the receiver.
Therefore, a need exists for a method and apparatus of adjusting the operation of an RSSI module to provide a more predictable range of operation, which, in turn, provides a more predictable range of operation for other components in the receiver and improves resolution.